Posted
by
Soulskillon Wednesday August 14, 2013 @08:12AM
from the if-they're-any-smaller-you-have-to-throw-them-back dept.

Hugh Pickens DOT Com writes "Long overlooked as mere rocky chunks leftover from the formation of the solar system, asteroids have recently gotten a lot more scrutiny as NASA moves forward with plans to capture, tow, and place a small asteroid somewhere near our planet. Two different private space companies, Planetary Resources and Deep Space Industries, plan to seek out and mine precious metals and water from near-Earth asteroids. Now Adam Mann reports that astronomers have identified 12 candidate Easily Retrievable Objects (EROs) ranging in size from approximately 2 meters to 60 meters in diameter that already come (cosmically) close enough to our planet — close enough that it would take a relatively small push to put them into orbits at Lagrange points near Earth using existing rocket technology. For example, 2006 RH120 could be sent into orbit at L2 by changing its velocity by just 58 meters per second with a single burn on 1 February 2021. Moving one of these EROs would be a 'logical stepping stone towards more ambitious scenarios of asteroid exploration and exploitation, and possibly the easiest feasible attempt for humans to modify the Solar System environment outside of Earth (PDF),' write the authors in Celestial Mechanics and Dynamical Astronomy. None of the 12 ERO asteroids are new to astronomers; in fact, one of them became briefly famous when it was found to be temporarily orbiting the Earth until 2007. But until now nobody had realized just how easily these bodies could be captured."

It doesn't have to hit Earth to affect it. Consider the tides. Our global eco system has evolved to expect tides. It would be difficult if not impossible to predict the full extent of the harm that could result if tidal patterns are altered. All sorts of life could flourish or die under such changes.

I'm not exactly a tree-hugger, but I certainly appreciate the factors and influences over life on this planet. This would affect the oceans in all sorts of ways. That which affects the oceans and the life within them will affect us and possibly even global weather patterns.

Because a 2~60m diameter stone in space can significantly alter tides.

that many of them i'd expect them to be largely equally spread out, or near enough to be considered such. as such, the effect would be close to nil, and the net effect would be zero. note also that this entirely ignores the problems of keeping a few thousand (or hundred thousand!!) objects orbiting the earth at tens of thousands of miles per hour without colliding, which they surely would, quickly forming a problem many orders of magnitude in excess of the current problems with space junk.

We are not just collecting them, the plan is to mine them. And what's this talk about hundreds or thousands? Even if asteroid mining becomes an industry, i doubt there will be more than 10 at a time. Eventually, they will learn to mine them on spot or use the Moon for it, without towing them to Earth.

Because a 2~60m diameter stone in space can significantly alter tides.

No, but once you start getting hundreds or thousands of them in near orbit, it might start having an effect that is noticeable in some places.

Have you any grasp of how big a difference 12 orders of magnitudes is? De you think "hundreds or thousands" is ANYWHERE near 1,000,000,000,000?

The world's population is roughly 6 billion, and that is just 6,000,000,000 (3 less zeros than above). If we have 1 such asteroid for every single person on Earth, the volume of these rocks would still be only less than 1% of the Moon.

Do you also worry that America will sink under the sea if a few thousand foreigners come to visit the US?

It doesn't have to hit Earth to affect it. Consider the tides. Our global eco system has evolved to expect tides. It would be difficult if not impossible to predict the full extent of the harm that could result if tidal patterns are altered. All sorts of life could flourish or die under such changes.

I'm not exactly a tree-hugger, but I certainly appreciate the factors and influences over life on this planet. This would affect the oceans in all sorts of ways. That which affects the oceans and the life within them will affect us and possibly even global weather patterns.

Because a 2~60m diameter stone in space can significantly alter tides.

The level of numerical illiteracy* of the general public (i.e. the GP) is appalling, and combined with the boatloads of self-esteem fed to them during school years, it resulted in people worse than being totally ignorant.

A totally ignorant person would either ask the above question without assumption, e.g. "Is it possible for the captured asteroid to affect the Earth in any meaningful way?", or just assume the experts have already thought about it. Only those who knew just enough to be dangerous would both assume their imagination (considerations that is not based on hard facts nor experience is no different than imagining things) is correct, AND the experts have not considered it already.

* - by that, I mean the lack of sense in numerical scales and numbers. The radius of the Moon is in the order of ~1000km, so a 60m asteroid (round to 100m) is 4 orders of magnitude in linear dimension and thus 12 orders of magnitude in volume. How lack of numerical sense do you need to be to think that something 12 orders of magnitude smaller can have any impact?

one thing you forgot to consider was distance, and the moon si really really far out there.

also, 12 orders of magnitude is 10^12. given that the moon is ~3474km in diameter (1700km radius), compared to a 60m object the moon is only 5.79e+4 times larger....which is no where near "12 orders of magnitude". but the size that we really need to consider isnt dimensional anyway, but mass.

so let's explore:

Remember the formula is F=G*m1*m2 / d^2. The gravitational force is inversely proportional to the square of the separation distance between the two. So we can hold the factors other than d unitary to determine the relative strengths at the following distances (truncated for space):~380k km (roughly the moon's average distance) = 6.925e-12~36000 km (typical geosynchronous orbit, ie, GPS) = 7.716e-10~2000 km (medium earth orbit) = 2.5e-7

So an object at MEO has 324x as much pull as the same object at typical geosynchronous distance, and >36000x as much pull as the same object at the moon's distance. So an object the size of the moon at the moons distance can have the same pull as an object 1/36000 the mass of the moon but in MEO*. Given the moon's mass is 7.3477e+22 kg, this gives us an equivalent mass of 2.041e18 kg at MEO, or 2.26e+20 kg at geosynchronous distance**. Then we can take the moons density of ~3346 kg/m^3. This gives us volumes of ~6.0998e+14 m^3 (MEO) and ~6.754e+16 m^3 (GS), which in turn give shperical diameters of 105.22 km (MEO) and 505.27 km (GS).

So we end up with objects only 0.0302 and 0.1454 the diameter of the moon at MEO and GS to have the same effect as the moon, assuming the same density as the moon. If we instead assume say an asteroid largely composed of Iron (density 7,870 km/m^3) we get diameters of ~79 and 380 km. An iridium asteroid is about the densest thing we might find out there, and even then our diameters calculate to ~56 and ~268 km.

So this is neat stuff, and now we get a real sense of what it would take to have an effect equivalent to the moon. But that's not to say there would no effect. while the distance relationship is an inverse square, the effect of mass is directly proportional, so something with half the mass will have half the effect. and while the poster mentioning hundreds of thousands of these things misses the logistical problems, having a sufficient number number of solid or metallic core examples of these things could have a measurable impact, particularly in terms of periodic reinforcement. and now im running out of time for thought experiment math (gotta get back to work).

*(force vector going to center of a theoretical main body, and thus ignoring for now the angles of distributed force vectors in the real situation being far different between an object in MEO and an object at the moons distance as they effect a fluid on the surface of said main body)**(ignoring for now the orbital velocities or distances required for such objects to remain in stable orbit)

Then let me finish for you. Given the numbers you calculated, the biggest object, with the highest reasonable density, in the closest orbit, would have one billionth the effect of the moon (60m vs 56km, cubed). So, in a place like the Bay of Fundy, with some of the largest tides in the world (16m), you still couldn't measure the difference with a ruler.

If we somehow manage to move enough matter into orbit to change the tides significantly then we have already demonstrated the technology to move the moon orbit to offset the change.

Do you realize how insane that sounds? Even if we scale up the space mining industry to dwarf the mining industry on earth we will not be anywhere close to change the tides more than the moons receding from the earth already does. (Yes, the moon isn't in a perfect orbit and the tidal forces are reduced for every year. The change

you did not do well in physics at school, did you? We're talking about L2 which is 3.9x times the distance to the moon, and tidal forces decrease as a third power of distance. even a *second moon* at L2 would only increase tidal force by 1.6%

1. What makes you think they would stop at 60m?2. What makes you think they would not collectively accumulate a lot more?

By your logic:

- One should never share one's M&Ms, because what makes you think the other person won't take the whole bag?- One should never bathe, because what makes you think you won't fall in and drown?- One should never, ever receive fellatio, because what makes you think she won't swallow you whole?

By my logic, we know that our energy lust leads to all sorts of environmental damage and serious health problems and we know that private enterprise which is largely responsible for all of it in one way or many require government oversight and limiting. We know that the same private enterprise lobbies with much success to have limits raised and lifted to futher their own interests at the expense of everyone else.

We know what people do -- especially business people. And to presume that we're not talking ab

There's stuff whizzing past us all the time with the gravitational attractive force that these rocks will have. It's not going to impact tidal patterns until we start capturing relatively large objects... like relative to the moon kind of size.

You know you only have to stand about 6 feet away from somebody to have the same gravitational pull on them as Mars has on you when it's closest to earth?Mars already impacts our tidal patterns more than these rocks.

you mention distance yet seem to ignore its effects. tides are also not uniform across the planet, nor isntantaneous, but depend on other factors such as local graviation (really big mountain or valley nearby), geography (affecting flow rate, such as wide open shore line vs being way up a long narrow fjord).

tides also are already affected by periodic reinforcement (ie, when sun and moon's gravities align and reinforce each other), so that's probably the biggest effect you would see of sufficient objects of

Looks like it's time to build a foundry in space so we can begin the construction of satellites, space stations and long range spacecraft with materials readily available in space, so we don't have to keep carting it up there. Between that and robots and assembly machines, we should be able to build out stuff in the next couple decades.

If you can think of a way to make a printer robot, with all it's moving pieces, electronics, etc... using nothing but rock and metal then you might have something there. I can't wait to see your motor windings made of rock insulated wire, asteroid derived lubricant, rock circuit boards, etc...

Electronics can be brought up from Earth, they're mostly small and light - at even $10k/pound delivery charge a cpu is only a few times more expensive than on Earth. A motor is a little pricier, especially a large high-power one if you needed such a thing, but still relatively cheap compared to a spacecraft. Most of the mass of any orbital structure will be (drumroll please) the structure. Girders, skin, shielding, etc. If we can print or otherwise manufacture a big reinforced steel can then the electron

That assumes a pretty solid structure - from what I've heard the guesses are that most asteroids are a bit closer to a gravel pile than a block of granite. Still, it would make excellent sense to use the rock as radiation and micrometeorite shielding, you just might have to mix it (at least the outer layers) with some sort of binding agent first so that it doesn't get torn apart under serious acceleration.

Bootstrap. A minimal set of tools sent into orbit to build a bigger set of tools. Two or three iterations can have large scale foundries up and running, while building some other interesting things along the way.

Most of the materials you need to build the bigger tools aren't on the asteroid so you're kind of SOL.

Right. Because iron, nickel, carbon, and silicates are rarely used in heavy industry.

If we had the technology to locate the raw materials, mine them, refine and process them, and then produce finished goods fully automatically we wouldn't use humans to mine anything on Earth anymore either.

Humans are cheap, and have political opinions. It probably wouldn't be that much of a technical challenge (compared

Looks like it's time to build a foundry in space so we can begin the construction of satellites, space stations and long range spacecraft with materials readily available in space, so we don't have to keep carting it up there. Between that and robots and assembly machines, we should be able to build out stuff in the next couple decades.

Time to start testing what a zero-g foundry should look and act like more likely. While we've done some fabrication and welding in space, I doubt we've tried the equivilent of anything like a foundry. Zero g and no atmosphere will make our usual methods unworkable. Hell, learning how to mine will be a huge undertaking with no gravity to hold bits down and collect them or for use as traction for vehicles or machinery. With the readily available solar power and energy, I suspect smaller rocks could be melted

Fuel's the only problem for unmanned space. Mass of the rest of the crap is trivial. Mining asteroids doesn't solve, or really address at all, the fuel problem.

Fuel is trivial too. The main problem is that all of it is sitting at the bottom of the planet's gravity well. Climbing out of that well requires big rockets, and big rockets are expensive to design and build. As far as fueling them, that is "in the noise" as they say: costing hundreds of thousands of dollars on a project that costs billions of dollars.

I would think that most of the volatile molecules like water would have been baked away over the millennia. If so, that would leave primarily rock and metal type asteroids. Further out, like the belts of the gas giants, the story would be different.

Sun-grazing asteroids perhaps, but most of them are very similar in composition to the early nebula since the only heating they have ever experienced is from collisions. That's why they're generally used as examples of what the planets originally coalesced out of. Apparently quite a few of them are from the cores of expired comets, which would mean that they probably include large amounts of frozen gasses as well. Since any of them that we get to touch have come through Earth's atmosphere first we can't

Actually lots of asteroids are apparently rich in ice and simple hydrocarbons - great raw material for synthesizing rocket fuel. The Moon's surface is similarly rich, and while you are at the bottom of a gravity well it's at least a much shallower well than Earth's, and without an appreciable atmosphere rail-gun launches into orbit are entirely feasible.

Moreover fuel is increasingly becoming an anachronism - ion drives blow everything else out of the water in terms of specific impulse, and they don't use f

>apparently...but of course - we can only plan from the best data we have available. That's why we do proof-of-concept projects like this, to see if our data and plans are actually viable.

>ion drives...I was actually being a bit forward looking there - we already have several ion drives in the lab that promise to compete in thrust/ton of engine with traditional rockets while reducing reaction mass drastically. I don't know that we'll have them in 2020, I'd bet more towards the latter half of the cen

I know the article talks in relative terms - but changing a massive object's velocity by 58 m/s is not trivial. Also, this assumes the asteroid isn't tumbling or rotating. You would have to cancel this before actually attempting to move the object.

That's well within the capability of a conventional rocket, just in terms of thrust. The problem would be figuring out how to grapple the object and stop its rotation. If it's only 5m wide, you could probably just throw some kind of net around it. I wouldn't be surprised to see plans to capture this particular object starting to appear in the near future.

Also, this assumes the asteroid isn't tumbling or rotating. You would have to cancel this before actually attempting to move the object.

Only if you need to attach 1 big rocket to object being captured.

You could use a gravity tub approach, although it probably needs a small target to work.

Or, you could put lots of smaller rockets all over the surface and just have them fire a quick pulse when they are facing the right way, that would have the added benefit of redundancy should a rocket fail.

"They calculate that this could be done with a single burn on 1 February 2021"

This doesn't sound like a relative term to me. And it was even mentioned in the summary too!I'm not sure I would go so far as to say this means it is objectively easy. I suppose landing a rocket engine on an asteroid and using it to push is something that has never been done before. That alone means there will be challenges to overcome. With only one push necessary though.. that's about as easy as one could realistically imagin

A shuttle is 4 and a half million pounds. and is fighting Earth's gravity. If the largest rock in the summary was picked, it'd weight less than 1 million pounds on Earth (more like half a million).Changing its velocity by 58m/s is actually technologically trivial. Rotation isn't so bad either, you just pulse your burners. The article just says single burn to give you a nice number.More than likely, they'd send up 3 - 6 rockets for redundancy and to stabilize the rock's rotation in a few bursts. Then they'd

It wouldn't surprise me that much if the first company to capture an asteroid finds all manner of space "junk" headed for it's installation, or perhaps the odd missile from the ground if countries feel threatened enough.

And what happens if, due to a malfunction, the thruster doesn't shut off when it's supposed to, and it burns for longer than 58 seconds?

People got angry about BP, and before that the Exxon Valdez, but that was after the accidents had already happened. What happens when a greedy grab for extraterrestrial ore inevitably goes awry? And make no mistake; over the long hault, it is inevitable. Even if the first attempt, hell the first five such attempts, go off without a hitch, there would eventually, over many such attempts, be a critical error on a similar mission.

And what happens if, due to a malfunction, the thruster doesn't shut off when it's supposed to, and it burns for longer than 58 seconds?

It would just run out of fuel. It is so expensive to hurl any mass into space that you do not take anything extra with you. The main thing that could go wrong is that the direction of the thrust is wrong or that you blow the asteroid to pieces.

Well, let's consider the damage from the impact of a rocky asteroid, 60m in diameter. Plug this into the excellent Earth Impact Effects program at http://impact.ese.ic.ac.uk/ImpactEffects/. Assume a velocity of 17 km/s, which they say is "typical for asteroids," and an impact angle of 45 degrees.

The calculator says:

The projectile begins to breakup at an altitude of 54000 meters = 177000 ft
The projectile bursts into a cloud of fragments at an altitude of 4700 meters = 15400 ft
The residual velocity of the projectile fragments after the burst is 4.77 km/s = 2.96 miles/s
The energy of the airburst is 4.52 x 1016 Joules = 1.08 MegaTons.
No crater is formed, although large fragments may strike the surface.

Clearly you wouldn't want to be right underneath it, but even as close as 20 km, the air blast effects seem rather anticlimactic:

And that's if it even hits Earth. If the rockets burn too long they may push the asteroid too far so that it gets flung out to space (gravitational slingshot around Earth). I'll worry if we decide to capture HUGE asteroids on our first go around, but 60 meters large asteroids seem to be an extremely low risk.

They are trying to hit an earth-sun lagrange point. If they do so, the object leaves its solar orbit and enters an unstable earth orbit. They then need to give it another few burns to stabilize the orbit (and keep it away from the lagrange point, which would allow it to leave earth orbit and resume orbiting the sun) . If they miss, then it travels on, on a different orbit, with roughly the same chance of hitting the earth as it ever did.

The asteroids being considered are roughly the size of the Chelyabinsk meteor. It's highly unlikely one would make it to the ground. You could still get a similar air-blast, but the odds are pretty good that it won't hit a populated area (remember, three-quarters of the Earth is water).

Perhaps you plan your burn so the asteroid is never on an earth intercepting trajectory? Shouldn't really be that hard. And if something goes really and truly wrong you detonate the rocket. It was good enough for all the live warhead nuclear missile tests we've done; aim away from anything important, keep your finger on the abort button.

There are some pretty simple engineering solutions for the problem. One quick example, give the ship 2 different fuel tanks (and possibly 2 different sets of thrusters) One fuel tank and thruster set gets us to the asteroid, at which point it shuts down. The 2nd set provide delta-v towards earth, only having enough fuel to get it into position (with maybe a bit extra, just in case... but not enough extra to crash into us)

In the long run, we'll probably move production away from earth. I wonder if Mars

This is insane. Let them first develop 100.00000000000%-reliable-accurate-faultless technology before putting the entire planet.. every lifing thing on or above earth.. at serious risk of vaporization.
These people ought to be institutionalized...

What risk? Even if we screwed up in the worst possible manner and it collided with the Earth (a vanishingly small probability within the space of all possible screw-ups, most of which would send it sailing merrily past us), a 60m asteroid traveling at roughly the same speed and direction as the Earth would be unlikely to reach the surface to leave a crater. Some fragments might, and you probably wouldn't want to be directly underneath the fireball as it burnt up/detonated in the atmosphere, but even then

This is insane. Let them first develop 100.00000000000%-reliable-accurate-faultless technology before putting the entire planet.. every lifing thing on or above earth.. at serious risk of vaporization.

The SpaceX Falcon Heavy is planned to deliver payload to low Earth orbit for the astoundingly low price of $709/lb. It's maximum payload to geosynchronous transfer orbit is less than half that to LEO (21 vs 53Mg), and I'm guessing the total launch cost is probably about the same, so call it $1800/lb. To Mars the maximum payload is 13Mg, or $2900/lb (which is actually much closer to last-years costs to LEO, so Mars is getting a lot more accessible than it used to be).

In all fairness, it does sound a wee bit like the start of disaster sci-fi movie. An interesting one even. Some asteroids, massive amounts of greed, a cute alien race risking their life and limb for our increasingly idiotic and helpless humanity.

Your a bunch of pussies 1. the asteroid sizes they're talking about would have no significant affect in any failure scenario, well perhaps if it actually HIT the ISS or a satellite but thats not likely. The size of asteroids they want to mine would almost entirely burn up in the atmosphere if it did miss and enter earth.

This is the exact thing we need to be doing we cant exist on earth forever, even if we had 0 environmental impact as a race the planet would eventually expire. Exploiting extra-planetary resources and colonizing space are the most important goals that could ever exist for us as a race. Only those things can provide us a chance at keeping the human race alive in perpetuity

If you have significant residue, then "bag it" and park it somewhere (e.g., nearby). If you need it again (including as reaction mass for a mass-driver), then it's to-hand. If you really need to tidy up the environment, drop it -60km/s of heliocentric delta-vee and it'll soon enough be plasma.

Remember that the Lagrangian points are "points" only when all of (Sun, Earth and Moon are perfect spheres) AND Jupiter and the rest of the Solar System don't exist AND lots of other things.

What percentage of these bodies has valuable metals? One thing to consider is that most of the economic deposits of the Pt-Group Metals, such as the Bushvesd, Skargard, and Stillwater Complexes are probably astroblems from the post Great Bonbardment era in which asteroids give the Earth their heavy metals after it had the heat to concentrate these in the core. They remained in the crust. This may also apply to Au and related metals as well.

The counter-intuitive reality is that, in an economically free society, people will solve problems faster than they become serious. This theory has successfully made predictions over 10 year periods over and over again.

The days of politics as memes figting in your brain should be over.

So yes, death to the false meme that we are ruining the planet, as vector to massive government control

The world was considerably more "economically free" during the times when the Cuyahoga River was spontaneously combusting, asbestos was being used to fireproof pretty much everything, and patent medicines were addicting tens of thousands of people to opiates. Don't really recall any phantasmagorical free market solutions to those (or many, many other) problems, do you?